Consider a system-on-chip (SoC) that supports multiple wireless standards such as Bluetooth (BT), wireless local-area network (WLAN), FM radio, GPS, etc. One or more of these wireless standards typically switch between an active and an idle mode. The periodic movement between active and idle modes could happen hundreds of time a second, and every such switch between active and idle mode (and vice-versa) causes a change in the current draw from the SoC power supply. Consequently, the power supply voltage, nominally constant, experiences a low-amplitude fluctuation at the frequency of the active-to-idle and idle-to-active switching activity.
The periodic fluctuation of the power supply to a multi-standard SoC sends a ripple through the on-chip electronics, and manifests itself as an audible and undesirable buzz in FM radio. The conventional and obvious method to treat this undesirable situation is to electrically isolate the different parts of the chip serving the different wireless standards. However, such techniques increase chip area, complexity, cost and power consumption.
Hence, it is desirable to have suppression of interference (noise) across transceivers integrated on a semiconductor chip.